A telecommunication network typically comprises a plurality of telecommunication sites distributed over the coverage area of the telecommunication network. Typically, each telecommunication site comprises a plurality of electrical and electronic apparatuses, such as:                telecommunication apparatuses (e.g. switches, routers, etc.);        auxiliary apparatuses which perform functions allowing the telecommunication apparatuses to operate (e.g. cable pressurizers, conditioners for keeping constant the temperature of the telecommunication apparatuses, etc.); and        other electrical apparatuses (e.g. air conditioners and heating systems for the offices, elevators, computers, lighting systems, etc.).        
The telecommunication apparatuses typically have a substantially constant electricity consumption, they require to be supplied with a DC current at a nominal voltage of 48 V, and their electricity supply can not undergo interruptions longer than few tens of milliseconds. On the other hand, auxiliary apparatuses and the other electrical apparatuses have an electricity consumption which significantly varies according to the seasons, the day of the week (either working day or holiday), and the time of the day.
Each telecommunication site is typically supplied by an electricity supply apparatus.
An electricity supply apparatus typically comprises a mains-generator switch, an energy station and one or more batteries. The mains-generator switch has two input lines which are connected to a mains and, optionally, to a generator, respectively, and an output line. The mains-generator switch is switchable between a normal operational status, wherein it draws an AC current from the mains, and a failure status (e.g. when a black-out occurs in the mains), wherein it can draw an AC current from the generator. The mains-generator switch then outputs the drawn AC current through its output line, which distributes it to the apparatuses of the telecommunication site.
In particular, the AC current is distributed partially to the energy station and partially to the auxiliary apparatuses and the other electrical apparatuses. The energy station, which substantially comprises a number of rectifiers, converts the AC current in a DC current at a nominal voltage of 48 V. The conversion performed by the energy station typically implies a conversion loss. However, for simplicity, in the following description it is assumed that the conversion efficiency of the energy station is substantially equal to 1, i.e. the conversion loss is substantially negligible.
In a first status, either the mains or the generator are able to supply a theoretically unlimited amount of current. If the batteries are substantially fully charged, the whole current supplied by the energy station is absorbed by the telecommunication apparatuses. If the batteries are only partially charged, the current supplied by the energy station is absorbed partially by the telecommunication apparatuses and partially by the batteries, which then recharge. In any case, in this first status, the amount of current that the energy station draws from the mains (or the generator) through the mains-generator switch only depends on the current absorbed by the loads (i.e. the telecommunication apparatuses and, if only partially charged, the batteries).
In a second status, e.g. due to a failure or a black-out, both the mains and the generator are able to supply a limited amount of current which is lower than the current required by the telecommunication apparatuses. In some cases, neither the mains nor the generator are able to provide any current at all. In this second status, the telecommunication apparatuses start to fully or partially draw the required current from the batteries, which then start to discharge.
The above described electricity supply apparatus may be used to supply not only a telecommunication site but, more generally, any industrial site having electrical and/or electronic apparatuses which, similarly to the above telecommunication apparatuses, have a substantially constant electricity consumption, require to be supplied with a DC current at a given nominal voltage, and whose electricity supply can not undergo interruptions longer than few tens of milliseconds.
Typically, the price of the electrical energy varies according to the day of the week and the time of the day. Therefore, the overall cost of the electrical energy drawn by an industrial site during a day is:
                              C          =                                    ∑                              i                =                1                            24                        ⁢                          pi              *              qi                                      ,                            [        1        ]            wherein pi is the price per hour of the electrical energy during the ith hour of the day and qi is the amount of electrical energy drawn by the industrial site during the ith hour of the day. Typically, the price per hour of the electrical energy varies on a supply-demand basis, i.e. it is lower during the night (i.e. when the electrical energy demand is lower) and it is higher during the day (i.e. when the electrical energy demand is higher).
U.S. Pat. No. 6,885,115 discloses a system and a power supply control method capable of having a peak shift function without deteriorating the essential function of an apparatus. The power supply system comprises a secondary battery for supplying power to a load circuit, a power receiving unit for receiving power externally provided to the load circuit, a switch for selectively supplying the power of the secondary battery or the power externally provided to the load circuit, and a controller for instructing the switch to stop the supply of the power externally provided to the load circuit for a predetermined time zone. By using the second battery, which is capable of storing the electric energy to the extent to show the essential function, it is possible to add the peak shift function to an apparatus. More specifically, by typically stopping or reducing power supply from a commercial power source while receiving the power necessary for operations of an apparatus from a built in battery, it is possible to realize peak shift.
U.S. Pat. No. 6,522,031 discloses a large scale, capacitor-based electrical energy storage and distribution system capable of effectuating load-levelling during periods of peak demand on a utility. A capacitor or multitude of capacitors may be charged with electrical energy produced by the utility during periods of low demand, such as the evening hours, and discharged during periods of high electrical energy consumption to help reduce demand on the utility. One or more capacitors may be located at a consumer's residence or business for providing at least a portion of the consumer's electrical power requirements. Alternatively, a farm of capacitors may be provided at or near a utility, or at or near a location experiencing high demand, such that electrical energy stored in the capacitors can be discharged into the utility's distribution grid to increase the amount of electrical energy available for use.
The paper “Some special devices used in the new type of power plants for the Italian telecommunications systems”, by M. Grossoni and F. Molinari, Proceedings of the 2nd International Telecommunications Energy Conference (INTELEC) 1979, discloses a technique which is termed “external limitation”. According to the external limitation technique, the rectifiers of the energy station are provided with a device that, on the basis of a remote control, controls the limitation of the output current of the rectifiers in order to avoid possible overloads of the generator.